Pedicle screw assembly having a retractable screw tip for facilitating the securement of the pedicle screw assembly to a spinal vertebra

ABSTRACT

A pedicle screw assembly has a retractable screw tip that facilitates the securement of the pedicle screw assembly to a spinal vertebra in a minimally invasive fashion during an orthopedic surgical procedure. The pedicle screw assembly includes a body portion including a head and a shank. The shank includes an outer surface with a thread provided thereon, an end having a cutting tip provided thereon, and a bore extending inwardly from the end and having an internally threaded region provided therein. The pedicle screw assembly also includes a tip portion including a body having a cutting edge and a shank extending from the body. The shank has an externally threaded region provided thereon that cooperates with the internally threaded region of the bore to permit movement of the tip portion relative to the body portion between extended and retracted positions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/086,447, filed Aug. 5, 2008, the disclosure of which is incorporatedherein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

This invention relates in general to fasteners that are used to securedevices to bones in surgical procedures. In particular, this inventionrelates to a pedicle screw assembly having a retractable screw tip thatfacilitates the securement of the pedicle screw assembly to a spinalvertebra in a minimally invasive fashion during an orthopedic surgicalprocedure.

Many surgical procedures involve the securement of a device to a bone.For example, during an orthopedic surgical procedure, it is oftennecessary to secure a support or alignment device to one or morevertebrae in the lumbar or thoracic region of the spine. The securementof such a device to the vertebra usually involves a series of relativelycomplex steps. For example, in one known procedure, a conventionalJamshidi needle (which includes a hollow outer cannula and an innerobturator having a tapered cutting edge) is initially inserted through arelatively small incision until the tapered cutting edge of theobturator engages a desired location on the surface of the vertebrawhere a fastener, such as a pedicle screw, is to be secured. The preciselocation where the tapered cutting edge of the obturator engages thesurface of the vertebra is usually determined using conventionalfluoroscopic or other imaging or navigational techniques.

Once the tapered cutting edge of the obturator has been positioned atthe desired location on the surface of the vertebra, a conventionalimpaction tool is used to advance the Jamshidi needle further within thevertebra so as to create a passageway therein. The depth of theinsertion of the Jamshidi needle within the vertebra can be determinedusing conventional fluoroscopic or other imaging or navigationaltechniques. Then, the obturator is removed from the Jamshidi needle,leaving behind the hollow outer cannula. A flexible guide wire is nextinserted through the hollow outer cannula of the Jamshidi needle untilthe leading end thereof extends through the passageway and is receivedwithin the body of the vertebra at a desired depth. The depth of theinsertion of the leading end of the guide wire within the body of thevertebra can be determined using conventional fluoroscopic or otherimaging or navigational techniques. Then, the hollow outer cannula ofthe Jamshidi needle is withdrawn from the vertebra, leaving the leadingend of the guide wire within the body of the vertebra.

A conventional cannulated threading tool is next inserted over thetrailing end of the guide wire and guided therealong to the relativelyshort passageway in the vertebra. The threading tool is used to tap athread within the passageway in the vertebra. The depth of the threadthat is tapped within the passageway can be determined usingconventional fluoroscopic or other imaging or navigational techniques.Next, the threading tool is withdrawn, and a cannulated pedicle screw isinserted over the trailing end of the guide wire. The pedicle screw isguided along the guide wire until a threaded tip of the pedicle screw isguided to the tapped passageway in the vertebra, again usingconventional fluoroscopic or other imaging or navigational techniques.The pedicle screw is secured to the vertebra by rotating it about theguide wire with a conventional tool, which causes the threaded tip ofthe pedicle screw to thread within the tapped passageway in thevertebra. Such rotation is continued until the pedicle screw has beendriven a predetermined distance into the body of the vertebra that,again, can be determined using conventional fluoroscopic or otherimaging or navigational techniques. Lastly, the guide wire is removed,leaving the pedicle screw secured to the vertebra, to which the supportor alignment device can be secured.

Although this procedure for securing a conventional pedicle screw to avertebra has functioned satisfactorily, it can be seen that thefluoroscopic or other imaging or navigational techniques are frequentlyemployed, which is time consuming and can result in significantradiation exposure. Thus, it would be desirable to provide an improvedstructure for a pedicle screw or similar fastener that avoids theseissues.

SUMMARY OF THE INVENTION

This invention relates to a pedicle screw assembly having a retractablescrew tip that facilitates the securement of the pedicle screw assemblyto a spinal vertebra in a minimally invasive fashion during anorthopedic surgical procedure. The pedicle screw assembly includes abody portion including a head and a shank. The shank includes an outersurface with a thread provided thereon, an end having a cutting tipprovided thereon, and a bore extending inwardly from the end and havingan internally threaded region provided therein. The pedicle screwassembly also includes a tip portion including a body having a cuttingedge and a shank extending from the body. The shank has an externallythreaded region provided thereon that cooperates with the internallythreaded region of the bore to permit movement of the tip portionrelative to the body portion between extended and retracted positions.

Various aspects of this invention will become apparent to those skilledin the art from the following detailed description of the preferredembodiments, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded side elevational view, partially in cross section,of a first embodiment of a pedicle screw assembly including a tipportion and a body portion in accordance with this invention.

FIG. 2 is an assembled side elevational view, partially in crosssection, of the first embodiment of the pedicle screw assemblyillustrated in FIG. 1, wherein the tip portion is shown in an extendedposition relative to the body portion.

FIG. 3 is an assembled side elevational view, partially in crosssection, of the first embodiment of the pedicle screw assemblyillustrated in FIG. 1, wherein the tip portion is shown in anintermediate position relative to the body portion.

FIG. 4 is an assembled side elevational view, partially in crosssection, of the first embodiment of the pedicle screw assemblyillustrated in FIG. 1, wherein the tip portion is shown in a retractedposition relative to the body portion.

FIG. 5 is a side elevational view of a modified tip portion that can beused with the pedicle screw assembly of this invention.

FIG. 6 is a side elevational view of a portion of a first modified bodyportion that can be used with the pedicle screw assembly of thisinvention.

FIG. 7 is a side elevational view of a portion of a second modified bodyportion that can be used with the pedicle screw assembly of thisinvention.

FIG. 8 is an assembled side elevational view, partially in crosssection, of a second embodiment of a pedicle screw assembly inaccordance with this invention.

FIG. 9 is an enlarged side elevational view of a tip portion of thesecond embodiment of the pedicle screw assembly illustrated in FIG. 8.

FIG. 10 is an assembled side elevational view, partially in crosssection, of a third embodiment of a pedicle screw assembly in accordancewith this invention.

FIG. 11 is an enlarged side elevational view of a tip portion of thethird embodiment of the pedicle screw assembly illustrated in FIG. 10.

FIG. 12 is an assembled side elevational view, partially in crosssection, of a fourth embodiment of a pedicle screw assembly inaccordance with this invention.

FIG. 13 is an enlarged side elevational view of a tip portion of thefourth embodiment of the pedicle screw assembly illustrated in FIG. 12.

FIG. 14 is an assembled side elevational view, partially in crosssection, of a fifth embodiment of a pedicle screw assembly in accordancewith this invention.

FIG. 15 is an assembled side elevational view, partially in crosssection, of a sixth embodiment of a pedicle screw assembly in accordancewith this invention.

FIG. 16 is an assembled side elevational view, partially in crosssection, of a seventh embodiment of a pedicle screw assembly inaccordance with this invention.

FIG. 17 is a sectional elevational view of a tip portion of the seventhembodiment of the pedicle screw assembly illustrated in FIG. 16.

FIG. 18 is a side elevational view, partially in cross section, of aninstallation tool as used as an impaction tool in connection with theembodiments of the pedicle screw assembly described above.

FIG. 19 is a side elevational view similar to FIG. 18 showing theinstallation tool as used as a rotation tool in connection with some ofthe embodiments of the pedicle screw assembly described above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, there is illustrated in FIGS. 1 through 4a first embodiment of a pedicle screw assembly, indicated generally at10, in accordance with this invention. As will be explained in detailbelow, the illustrated pedicle screw assembly 10 can be used tofacilitate the securement of a device to a bone. However, the pediclescrew assembly 10 of this invention may be used for any desired purposeor in any desired surgical procedure.

The first embodiment of the pedicle screw assembly 10 includes a bodyportion, indicated generally at 11, having a head 12 provided at a firstend thereof and an elongated shank 13 that extends from the head portion12. The body portion 11 of the pedicle screw assembly 10 may be formedfrom any desired material, such as titanium, stainless steel,cobalt-chrome, or other medically-approved biomaterial. In theillustrated embodiment, the head 12 of the body portion 11 is generallysemi-spherical in shape. However, the head 12 may be formed having anydesired shape. A conventional tulip or yoke (a portion of which is shownat 12 a) may be provided on the head 12 of the first embodiment of thepedicle screw assembly 10. Typically, the inner surface of the tulip 12a has an internal thread 12 b provided thereon, the purpose of whichwill be described below. However, it will be appreciated that the head12 and the tulip 12 a of the pedicle screw assembly 10 may be formedhaving any desired structures. The illustrated semi-spherical head 12and the associated tulip 12 a function in the nature of a universaljoint to provide a poly-axial pedicle screw assembly 10. If desired, thepedicle screw assembly 10 may be mono-axial, having a fixed orunidirectional head permitting movement along one axis only. The shank13 of the body portion 11 has an outer surface that is provided with ahelical or similar thread 13 a. The purpose for this thread 13 a will beexplained below.

The body portion 11 of the first embodiment of the pedicle screwassembly 10 has a second end that terminates in a cutting tip 14. Thecutting tip 14 may be embodied as any desired shape or structure (orcombination of shapes or structures) that can remove bone material froma vertebra (not shown) when rotated relative thereto. The second end ofthe body portion 11 also has a bore provided therein that that extendsinwardly from the cutting tip 14. The illustrated bore is generallyhollow and cylindrical in shape and includes a first non-threaded region15, a relatively large diameter internally threaded region 16, a secondnon-threaded region 17, and a relatively small diameter internallythreaded region 18. The purposes for each of these regions 15 through 18of the bore will be explained below.

The first embodiment of the pedicle screw assembly 10 also includes atip portion, indicated generally at 20. The tip portion 20 of the firstembodiment of the pedicle screw assembly 10 may also be formed from anydesired material, such as titanium, stainless steel, cobalt-chrome, orother medically-approved biomaterial. In this first embodiment of thepedicle screw assembly 10, the tip portion 20 is embodied as aself-drilling tip having a body 21 that includes a drill tip cuttingedge 22 and a clearance cutting edge 23. An elongated shank 25 extendsfrom the body 21 and has both a relatively large diameter externallythreaded region 26 and a relatively small diameter externally threadedregion 27 provided thereon. The purposes for each of these structuresand regions 22 through 27 of the tip portion 20 will also be explainedbelow.

If desired, the outer surface of the body 21 may be formed having anon-circular cross-sectional shape. As shown in FIG. 1, thisnon-circular cross-sectional shape may be embodied as one or moregrooves 21 a (shown only in FIG. 1) that extend outwardly from the outersurface of the body 21. Alternatively, this non-circular cross-sectionalshape may be embodied as one or more projections, ridges, or any otherstructure or combination of structures provided the outer surface of thebody 21. Additionally, this non-circular cross-sectional shape may beinherent in the cross-sectional shape of the body 21, which may berectangular, oval, or any other non-circular cross-sectional shape. Thepurpose for this non-circular cross-sectional shape will be explainedbelow.

Referring now to FIG. 2, the first embodiment of the pedicle screwassembly 10 is assembled by initially inserting the elongated shank 25of the tip portion 20 within the bore provided in the second end of thebody portion 11. The outer diameters defined by the relatively largeexternally threaded region 26 and the relatively small externallythreaded region 27 of the tip portion 20 are preferably both smallerthan the inner diameter defined by the first non-threaded region 15 ofthe bore provided in the second end of the body portion 11. Thus, therelatively large externally threaded region 26 and the relatively smallexternally threaded region 27 of the tip portion 20 both pass freelythrough the first non-threaded region 15 of the bore as the tip portion20 is initially inserted within the bore. However, the outer diameterdefined by the body 21 of the tip portion 20 is preferably sized suchthat it is journaled on the first non-threaded region 15 concentricallywithin the bore for free sliding movement relative thereto.

The outer diameter defined by the relatively small externally threadedregion 27 of the tip portion 20 is also preferably somewhat smaller thanthe inner diameter defined by the relatively large internally threadedregion 16 of the bore provided in the second end of the body portion 11.Thus, as the elongated shank 25 of the tip portion 20 is continued to beinserted within the bore provided in the second end of the body portion11, the relatively small externally threaded region 27 of the tipportion 20 passes freely through the relatively large internallythreaded region 16 of the bore provided in the second end of the bodyportion 11.

However, the outer diameter defined by the relatively large externallythreaded region 26 of the tip portion 20 is approximately the same asthe inner diameter defined by the relatively large internally threadedregion 16 of the bore provided in the second end of the body portion 11.Thus, as shown FIG. 2, the relatively large externally threaded region26 of the tip portion 20 will engage the relatively large internallythreaded region 16 of the bore provided in the second end of the bodyportion 11. Thereafter, rotation of the tip portion 20 relative to thebody portion 11 causes the relatively large externally threaded region26 of the tip portion 20 to cooperate with the relatively largeinternally threaded region 16 of the bore provided in the second end ofthe body portion 11, as shown in FIG. 2. When the relatively largeexternally threaded region 26 of the tip portion 20 cooperates with therelatively large internally threaded region 16 of the bore, the tipportion 20 is supported at an extended position relative to the bodyportion 11. In this extended position, the tip portion 20 is extendedbeyond the cutting tip 14 of the second end of the body portion 11. Thepurpose for supporting the tip portion 20 in this extended positionrelative to the body portion 11 will be explained below.

Further rotation of the tip portion 20 relative to the body portion 11causes the tip portion 20 to be withdrawn within the bore provided inthe second end of the body portion 11. As shown in FIG. 3, the tipportion 20 can be moved to an intermediate position relative to the bodyportion 11, wherein part of the tip portion 20 is located within thesecond end of the body portion 11, but the drill tip cutting edge 22 andthe clearance cutting edge 23 of the tip portion 20 are still extendedbeyond the cutting tip 14 of the second end of the body portion 11. Inthis intermediate position, both the relatively large externallythreaded region 26 and the relatively small externally threaded region27 of the tip portion 20 may be completely received within the secondnon-threaded region 17 of the bore provided in the second end of thebody portion 11, although such is not required. When received in thismanner, however, a relative small amount of axial sliding movement mayfreely occur between the tip portion 20 and the body portion 11. Thepurpose for supporting the tip portion 20 in this intermediate positionrelative to the body portion 11 will also be explained below.

The outer diameter defined by the relatively small externally threadedregion 27 of the tip portion 20 is approximately the same as the innerdiameter defined by the relatively small internally threaded region 18of the bore provided in the second end of the body portion 11. Thus, asshown FIG. 4, the relatively small externally threaded region 27 of thetip portion 20 will engage the relatively small internally threadedregion 18 of the bore provided in the second end of the body portion 11.Thereafter, rotation of the tip portion 20 relative to the body portion11 causes the relatively small externally threaded region 27 of the tipportion 20 to cooperate with the relatively small internally threadedregion 18 of the bore provided in the second end of the body portion 11.Thus, as shown in FIG. 4, the tip portion 20 can be supported at aretracted position relative to the body portion 11. In this retractedposition, the drill tip cutting edge 22 and the clearance cutting edge23 of the tip portion 20 are aligned with the cutting tip 14 of thesecond end of the body portion 11 to provide a complete drill tip.Alternatively, in this retracted position, the drill tip cutting edge 22and the clearance cutting edge 23 of the tip portion 20 may becompletely retracted within the cutting tip 14 of the second end of thebody portion 11. The purpose for supporting the tip portion 20 in thisretracted position relative to the body portion 11 will be explainedbelow.

As mentioned above, many orthopedic and other surgical proceduresinvolve the securement of a pedicle screw or a similar fastener into abone, such as a vertebra that is located in the lumbar or thoracicregions of the spine. The pedicle screw assembly 10 of this inventionprovides a mechanism for facilitating the securement of a pedicle screwto a vertebra that involves a substantially lesser number of steps thanis known in the art. To accomplish this, the tip portion 20 of thepedicle screw assembly 10 is pre-assembled onto the body portion 11 inthe extended position illustrated in FIG. 2, as described above. Then,using any desired tool, the pedicle screw assembly 10 is then insertedthrough a relatively small incision until the drill tip cutting edge 22of the tip portion engages the surface of the desired vertebra at alocation where the pedicle screw is desired to be secured. The preciselocation where the drill tip cutting edge 22 engages the surface of thevertebra can be determined using conventional fluoroscopic or otherimaging or navigational techniques.

Once the drill tip cutting edge 22 has been located at a desiredlocation on the surface of the vertebra, the pedicle screw assembly 10is then advanced further within a pedicle portion of the vertebra, suchas by using a conventional impaction tool (see FIG. 18) so as to createa hole in the vertebra. During the use of this impaction tool, therelatively large externally threaded region 26 of the tip portion 20cooperates with the relatively large internally threaded region 16 ofthe bore. The cooperation of these relatively large internally andexternally threaded regions 16 and 26 provide sufficient strength toendure the impact forces created by the impaction tool.

The extended tip portion 20 of the pedicle screw assembly 10 can beguided into the pedicle of the vertebra by conventional fluoroscopic orother imaging or navigational techniques by use of appropriate impactionforces on the head 12 thereof. The ideal point for location of the tipportion 20 is just past the pedicle into the vertebral body, at whichtime the cutting edge 14 of the body portion 11 is resting on theexternal surface of the vertebra. A broad cutting surface 14 preventsfurther impaction and undesirable advancement of the modified tip 20into the vertebral body. At this point, second phase of the insertion ofthe pedicle screw assembly 10 is begun, as described in detail below.

After the drill tip cutting edge 22 has formed the hole in the vertebra,the impaction tool is removed and the body portion 11 of the pediclescrew assembly 10 is rotated. Such rotation may be effected by means ofany conventional tool (see FIG. 19). During such rotation of the bodyportion 11 of the pedicle screw assembly 10, the drill tip cutting edge22 of the tip portion 20 remains stationary because of friction betweenit and the bone of the vertebra. Alternatively, the drill tip cuttingedge 22 of the tip portion 20 remains stationary because of thenon-circular cross-sectional shape of the body 21, such as by virtue offriction or the grooves 21 a or other structures discussed above. In anyevent, the rotation of the body portion 11 of the pedicle screw assembly10 occurs relative to the tip portion 20 thereof.

Consequently, the tip portion 20 is drawn within the bore of the bodyportion 11 of the pedicle screw assembly 10 until it reaches theintermediate position illustrated in FIG. 3. In this intermediateposition, the relatively large externally threaded region 26 of the tipportion 20 is disengaged from the relatively large diameter internallythreaded region 16 of the body portion 11. Additionally, the relativelysmall externally threaded region 27 of the tip portion 20 has not yetbecome engaged with the relatively small diameter internally threadedregion 18 of the body portion 11. The provision of this intermediateposition insures that the rotational movement of the tip portion 20relative to the body portion 11 is not impeded by the simultaneousengagement of both the relatively large threaded regions 16 and 26 andthe relatively small internally threaded regions 18 and 27 of the tipportion 20 and the body portion 11.

Further rotation of the body portion 11 of the pedicle screw assembly 10relative to the tip portion 20 causes the tip portion 20 to be furtherwithdrawn within the bore of the body portion 11 of the pedicle screwassembly 10 until it reaches the retracted position illustrated in FIG.4. In this retracted position, the relatively small externally threadedregion 27 of the tip portion 20 is engaged with the relatively smalldiameter internally threaded region 18 of the body portion 11. In thefinal retracted position, the drill tip cutting edge 22 and theclearance cutting edge 23 of the tip portion 20 are safely housed withinthe shank 13 of the body portion 11. Thereafter, the shank 13 of thebody portion 11 can be further advanced within the vertebra to thedesired depth by continued rotation. As the shank 13 of the body portion11 is continued to be rotated, its cutting edge 14 starts cuttingthreads in bone. At the same time, the helical thread 13 a provided onthe outer surface of the shank 13 of the body portion 11 forms aninternal tap within the hole formed in the vertebra. To accomplish this,the helical thread 13 a provided on the outer surface of the shank 13may have a self-tapping feature provided thereon, at least for apredetermined distance inwardly from the cutting tip 14. In its finalresting position, the tip portion 20 becomes permanently housed withinthe shank 13 of the body portion 11 and is left within the vertebraafter installation of the pedicle screw assembly 10.

It should be understood that other tip configurations, such aspyramidal, diamond, conical, spear, or any other desired shape orcombination of shapes may be chosen to facilitate advancement of the tipportion 20 within the vertebra with impaction and to resist rotationalforces as the body portion 11 is advanced over the tip portion 20. Also,the tip portion 20 may be formed having different diameters. In general,a smaller diameter pedicle screw assembly 10 will have a tip portion 20with reduced diameter, as compared with a thicker diameter pedicle screwassembly. The thread length, pitch, and other attributes of both therelatively large diameter externally threaded region 26 and therelatively small diameter externally threaded region 27 may also vary toensure retention of the tip portion in the extended position during theinitial impaction process and to ensure movement of the tip portion 20to the retracted position as the body portion 11 is advanced over thetip portion 20 during the rotation thereof, as described above. In theextended position, the tip portion 20 may extend any desired distancefrom the cutting tip 14, such as in the range of from about fivemillimeters to about twenty-five millimeters for example. Typically, ashorter length (such as is usually necessary in thoracic spine orpatients with smaller vertebrae) would require the tip portion 20 to beprojecting out of the body portion 11 for a shorter distance in theextended position. Conversely, longer extensions of the tip portion 20would be desirable for use in lumbar spine and in patients with biggervertebrae.

FIG. 5 illustrates a modified tip portion, indicated generally at 20′,that can be used with the pedicle screw assembly 10 of this invention.The modified tip portion 20′ is similar to the tip portion 20 describedabove, and like reference numbers are used to indicate similar parts.The modified tip portion 20′ is embodied as a beveled tip having a body21′ that includes a beveled tip edge 22′. An elongated shank 25′ extendsfrom the body 21′ and has both a relatively large diameter externallythreaded region 26′ and a relatively small diameter externally threadedregion 27′ provided thereon. The modified tip portion 20′ cooperateswith the body portion 11 of the pedicle screw assembly 10 in the samegeneral manner as described above, being movable between extended,intermediate, and retracted positions.

FIG. 6 illustrates a portion of a first modified body portion, indicatedgenerally at 11′, that can be used with the pedicle screw assembly 10 ofthis invention. The first modified body portion 11′ is similar to thebody portion 11 described above, and like reference numbers are used toindicate similar parts. The first modified body portion 11′ includes ahead (not shown) provided at a first end thereof and an elongated shank13′ that extends from the head portion and terminates in a cutting tip14′. The shank 13′ of the first modified body portion 11′ has an outersurface that is provided with a helical or similar thread 13 a′.Additionally, however, the helical thread 13 a′ has a relatively finepitch lead portion 13 b′. Such lead portion 13 b′ of the thread 13 a′initially engages the pedicle of the vertebra when the first modifiedbody portion 11′ is initially rotated relative thereto and can assist inproviding precise control of the retraction of the tip portion 20 withinthe shank 13′. A significant differential in the pitch of the relativelylarge diameter externally threaded region 26 and the relatively smalldiameter externally threaded region 27 on the tip portion 20 and thethread 13′ on the first modified body portion 11′ may lead to internalbinding and friction at the interface between the two components,causing an undesirable continued advancement of the modified tip portion20 anteriorly with penetration of the anterior vertebral cortex. Thisdual thread portion formed with a relatively fine pitch 13 b′ closer tothe pitch of the relatively large diameter externally threaded region 26and the relatively small diameter externally threaded region 27 of themodified screw tip 20 will ensure reliable retraction of the tip portion20 within the shank 13′. Thereafter, the normal helical thread 13 a′ ofthe first modified body portion 11′ with a higher lead would facilitatea faster insertion of the remainder of the shank 13′.

FIG. 7 illustrates a portion of a second modified body portion,indicated generally at 11″, that can be used with the pedicle screwassembly 10 of this invention. The second modified body portion 11″ isalso similar to the first modified body portion 11′ described above, andlike reference numbers are used to indicate similar parts. The secondmodified body portion 11″ includes a head (not shown) provided at afirst end thereof and an elongated shank 13″ that extends from the headportion and terminates in a cutting tip 14″. The shank 13″ of the secondmodified body portion 11″ has an outer surface that is provided with ahelical or similar thread 13 a″. Additionally, however, the helicalthread 13 a″ has a relatively fine pitch lead portion 13 b″. Such leadportion 13 b″ of the thread 13 a″ initially engages the pedicle of thevertebra when the first modified body portion 11″ is initially rotatedrelative thereto and can assist in providing precise control of theretraction of the tip portion 20 within the shank 13″ as describedabove. Furthermore, a tapered or conical transition portion 13 c″ isprovided between the helical thread 13 a″ and the lead portion 13 b″thereof. Otherwise, the second modified body portion 11″ functionssimilarly to the first modified body portion 11′.

FIGS. 8 and 9 illustrate a second embodiment of a pedicle screwassembly, indicated generally at 30, in accordance with this invention.The second embodiment of the pedicle screw assembly 30 includes a bodyportion, indicated generally at 31, having a head 32 provided at a firstend thereof and an elongated shank 33 that extends from the head portion32. The shank 33 of the body portion 31 has an outer surface that isprovided with a helical or similar thread 33 a. The body portion 31 ofthe second embodiment of the pedicle screw assembly 30 has a second endthat terminates in a cutting tip 34. The second end of the body portion31 also has a bore provided therein that that extends inwardly from thecutting tip 34, including a first non-threaded region 35, a relativelylarge diameter internally threaded region 36, a second non-threadedregion 37, and a relatively small diameter internally threaded region38. In this second embodiment of the pedicle screw assembly 30, however,the bore continues completely through the body portion 31. In theillustrated embodiment, this through bore includes a reduced diameterportion 39 a that extends from the relatively small diameter internallythreaded region 38 and an enlarged diameter portion 39 b that extendsfrom the reduced diameter portion 39 a.

The second embodiment of the pedicle screw assembly 30 also includes atip portion, indicated generally at 40. In this second embodiment of thepedicle screw assembly 30, the tip portion 40 is embodied as aself-drilling tip having a body 41 that includes a drill tip cuttingedge 42 and a clearance cutting edge 43. However, the tip portion 40 mayalternatively include a beveled tip that includes a beveled tip edge,such as shown in FIG. 5, or any other desired shape or structure asdiscussed above. An elongated shank 45 extends from the body 41 and hasboth a relatively large diameter externally threaded region 46 and arelatively small diameter externally threaded region 47 providedthereon.

In this second embodiment of the pedicle screw assembly 30, however, thetip portion 40 additionally includes an elongated extension 48 thatterminates in an enlarged end 49. The enlarged end 49 defines an outerdiameter that is larger than the reduced diameter portion 39 a of thebore formed through the body portion 41, but is smaller than theenlarged diameter portion 39 b of such bore. To assemble the secondembodiment of the pedicle screw assembly 30, the tip portion 40 isinitially provided in two separate parts, namely, a first part includingthe body 41, the shank 45, and the externally threaded regions 46 and 47and a second part including the elongated extension 48 and the enlargedend 49. The first part of the tip portion 40 can be installed within thebody portion 30 in the same manner as described above. Thereafter, theelongated extension 48 can be secured to the shank 45 of the tip portion40 by any desired means. For example, the elongated extension 48 can besecured to the shank 45 by press fitting, welding, threading, adhesive,and the like. Alternatively, the second embodiment of the modified screwassembly 30 may be assembled as follows. The tip portion 40 is initiallyprovided in two separate parts, namely, a first part (including the body41, the shank 45, and the externally threaded regions 46 and 47 as wellas the elongated extension 48) and a second part (including only theenlarged end 49). The first part of the tip portion 40 can be installedwithin the body portion 30 in the same manner as described above.Thereafter, the enlarged end 49 can be secured to the elongatedextension 48 of the tip portion 40 by any desired means, such as bypress fitting, welding, threading, adhesive, and the like. Regardless,when so secured, the enlarged end 49 functions as a stop to positivelyprevent the tip portion 40 of the second embodiment of the pedicle screwassembly 30 from being removed from the body portion 31 thereof.Otherwise, the second embodiment of the pedicle screw assembly 30functions in a manner similar to the first embodiment of the pediclescrew assembly 10 described above.

FIGS. 10 and 11 illustrate a third embodiment of a pedicle screwassembly, indicated generally at 50, in accordance with this invention.The third embodiment of the pedicle screw assembly 50 includes a bodyportion, indicated generally at 51, having a head 52 provided at a firstend thereof and an elongated shank 53 that extends from the head portion52. The shank 53 of the body portion 51 has an outer surface that isprovided with a helical or similar thread 53 a. The body portion 51 ofthe third embodiment of the pedicle screw assembly 50 has a second endthat terminates in a cutting tip 54. The second end of the body portion51 also has a bore provided therein that that extends inwardly from thecutting tip 54, including a first non-threaded region 55, a relativelylarge diameter internally threaded region 56, a second non-threadedregion 57, and a relatively small diameter internally threaded region58. In this third embodiment of the pedicle screw assembly 50, however,the bore 59 continues completely through the body portion 51.

The third embodiment of the pedicle screw assembly 50 also includes atip portion, indicated generally at 60. In this third embodiment of thepedicle screw assembly 50, the tip portion 60 is embodied as aself-drilling tip having a body 61 that includes a drill tip cuttingedge 62 and a clearance cutting edge 63. However, the tip portion 60 mayalternatively include a beveled tip that includes a beveled tip edge,such as shown in FIG. 5, or any other desired structure as discussedabove. An elongated shank 65 extends from the body 41 and has both arelatively large diameter externally threaded region 66 and a relativelysmall diameter externally threaded region 67 provided thereon.

In this third embodiment of the pedicle screw assembly 50, however, therelatively small externally threaded region 67 extends axially furtheralong the tip portion 60 than in the previous embodiments. Specifically,the axial length of the relatively small externally threaded region 67is sufficiently long that when the tip portion 60 is initially insertedwithin the body portion 51, the relatively small externally threadedregion 67 engages the relatively small internally threaded region 58provided within the bore of the body portion 51. Thus, further rotationof the tip portion 60 is necessary for the relatively large externallythreaded region 66 to engage the relatively large internally threadedregion 56 of the body portion 51 and thereby locate the tip portion 60.This extended axial length of the relatively small externally threadedregion 67 insures that the tip portion 60 is always threaded into thebody portion 51 to positively prevent the tip portion 60 of the secondembodiment of the pedicle screw assembly 50 from being removed from thebody portion 31 thereof.

The tip portion 60 additionally includes an elongated extension 68 thatterminates in an end 69. The end 69 has a drive mechanism providedtherein that is adapted to cooperate with a conventional rotation tool(see FIG. 19) to effect rotation of the tip portion 60 relative to thebody portion 51. In the illustrated embodiment, the drive mechanism is aslot 69 a that can cooperate with a conventional flat-head screwdriver.However, the drive mechanism can be embodied as any conventionalstructure for accomplishing this purpose. The elongated extension 68 andthe end 69 can be formed integrally with the remainder of the tipportion 61 or can be formed separately and secured thereto, as describedabove. Otherwise, the third embodiment of the pedicle screw assembly 50functions in a manner similar to the embodiments of the pedicle screwassembly 10 and 30 described above.

FIGS. 12 and 13 illustrate a fourth embodiment of a pedicle screwassembly, indicated generally at 70, in accordance with this invention.The fourth embodiment of the pedicle screw assembly 70 includes a bodyportion, indicated generally at 71, having a head 72 provided at a firstend thereof and an elongated shank 73 that extends from the head portion72. The shank 73 of the body portion 71 has an outer surface that isprovided with a helical or similar thread 73 a. The body portion 71 ofthe fourth embodiment of the pedicle screw assembly 70 has a second endthat terminates in a cutting tip 74. The second end of the body portion71 also has a bore provided therein that that extends inwardly from thecutting tip 74, including a first non-threaded region 75, a relativelylarge diameter internally threaded region 76, a second non-threadedregion 77, and a relatively small diameter internally threaded region78. In this fourth embodiment of the pedicle screw assembly 70, however,the bore continues completely through the body portion 71. In theillustrated embodiment, this through bore includes a reduced diameterportion 79 a that extends from the relatively small diameter internallythreaded region 78 and an enlarged diameter portion 79 b that extendsfrom the reduced diameter portion 79 a.

The fourth embodiment of the pedicle screw assembly 70 also includes atip portion, indicated generally at 80. In this fourth embodiment of thepedicle screw assembly 70, the tip portion 80 is embodied as aself-drilling tip having a body 81 that includes a drill tip cuttingedge 82 and a clearance cutting edge 83. However, the tip portion 80 mayalternatively include a beveled tip that includes a beveled tip edge,such as shown in FIG. 5, or any other desired structure as describedabove. An elongated shank 85 extends from the body 81 and has both arelatively large diameter externally threaded region 86 and a relativelysmall diameter externally threaded region 87 provided thereon.

In this fourth embodiment of the pedicle screw assembly 70, however, thetip portion 80 additionally includes an elongated extension 88 thatterminates in an enlarged end 89. The enlarged end 89 defines an outerdiameter that is larger than the reduced diameter portion 79 a of thebore formed through the body portion 71, but is smaller than theenlarged diameter portion 79 b of such bore. Additionally, the enlargedend 89 has a drive mechanism provided therein that is adapted tocooperate with a conventional rotation tool (see FIG. 19) to effectrotation of the tip portion 80 relative to the body portion 71. In theillustrated embodiment, the drive mechanism is a slot 89 a that cancooperate with a conventional flat-head screwdriver. However, the drivemechanism can be embodied as any conventional threaded or non-threadedstructure for accomplishing this purpose. The elongated extension 88 andthe end 89 can be formed integrally with the remainder of the tipportion 81 or can be formed separately and secured thereto, as describedabove. Otherwise, the fourth embodiment of the pedicle screw assembly 70functions in a manner similar to the embodiments of the pedicle screwassembly 10, 30, and 50 described above.

FIG. 14 illustrates a fifth embodiment of a pedicle screw assembly,indicated generally at 70′, in accordance with this invention. The fifthembodiment of the pedicle screw assembly 70′ is similar to the fourthembodiment 70 described above, and like reference numbers are used toindicate similar parts. In this fifth embodiment of the pedicle screwassembly 70′, however, the second non-threaded region 77′ of the bodyportion 81′ has an extended non-threaded region 77 a′ provided thereon.Similarly, an extended non-threaded region 86 a′ is provided between therelatively large externally threaded region 86′ and the relatively smallexternally threaded region 87′ provided on the tip portion 81′. Theextended non-threaded regions 77 a′ and 86 a′ are provided to facilitatethe installation of the tip portion 80′ within the bore of the bodyportion 71′. Otherwise, the fifth embodiment of the pedicle screwassembly 70′ functions in a manner similar to the fourth embodiment ofthe pedicle screw assembly 70 described above.

FIG. 15 illustrates a sixth embodiment of a pedicle screw assembly,indicated generally at 70″, in accordance with this invention. The sixthembodiment of the pedicle screw assembly 70″ is similar to the fifthembodiment 70′ described above, and like reference numbers are used toindicate similar parts. In this sixth embodiment of the pedicle screwassembly 70″, however, the thread 73 a″ provided outer surface of theshank 73″ of the body portion 71″ has an enlarged diameter region 73 b″located adjacent to the head 72″. The enlarged diameter region 73 b″ ofthe thread 73″ is provided to increase the diameter of the hole formedin the vertebra adjacent to the surface thereof, which would allow theuse of a pedicle screw having a correspondingly larger diameter threadedportion, thereby increasing the strength of the connection between thepedicle screw and the vertebra. Otherwise, the sixth embodiment of thepedicle screw assembly 70′ functions in a manner similar to the fifthembodiment of the pedicle screw assembly 70 described above.

FIGS. 16 and 17 illustrate a seventh embodiment of a pedicle screwassembly, indicated generally at 100, in accordance with this invention.The seventh embodiment of the pedicle screw assembly 100 includes a bodyportion, indicated generally at 101, having a head 102 provided at afirst end thereof and an elongated shank 103 that extends from the headportion 102. The shank 103 of the body portion 101 has an outer surfacethat is provided with a helical or similar thread 103 a. The bodyportion 101 of the seventh embodiment of the pedicle screw assembly 100has a second end that terminates in a cutting tip 104. The second end ofthe body portion 101 also has a bore provided therein that that extendsinwardly from the cutting tip 104, including a first non-threaded region105, an internally threaded region 106, and a second non-threaded region107. In this seventh embodiment of the pedicle screw assembly 100,however, the bore continues completely through the body portion 101. Inthe illustrated embodiment, the first non-threaded region 105 defines asmaller internal diameter than the second non-threaded region 107.However, such is not required.

The seventh embodiment of the pedicle screw assembly 100 also includes atip portion, indicated generally at 110. In this seventh embodiment ofthe pedicle screw assembly 100, the tip portion 110 is embodied as aself-drilling tip having a body 111 that includes a drill tip cuttingedge 112 and a clearance cutting edge 113. However, the tip portion 110may alternatively include a beveled tip that includes a beveled tipedge, such as shown in FIG. 5, or any other desired structure asdiscussed above. An elongated shank 114 extends from the body 111 and isexternally threaded throughout. The externally threaded elongated shank114 cooperates with the internally threaded region 106 of the boreformed through the body portion 101. Otherwise, the seventh embodimentof the pedicle screw assembly 100 functions in a manner similar to theembodiments of the pedicle screw assembly described above.

FIGS. 18 and 19 schematically illustrate an installation tool, indicatedgenerally at 140, that can be used in connection with the variousembodiments of the pedicle screw assembly described above. As will beexplained in detail below, the installation tool 140 can function bothas an impaction tool (which is used to advance the extended tip portionof the pedicle screw assembly within the pedicle of the vertebra) and asa rotation tool (which is used to effect rotation of the tip portion ofthe pedicle screw assembly relative to the body portion).

The illustrated installation tool 140 includes an elongated hollow body141 having a first end and a second end. The first end of the body 141has an externally threaded portion 141 a that extends from an engagementsurface 141 b. The second end of the body 141 has an impaction surface141 c. A passageway 141 d extends through the body 141 of theinstallation tool 140 from the externally threaded portion 141 a to theimpaction surface 141 c. The externally threaded portion 141 a of thebody 141 is preferably sized and shaped to cooperate with the internalthread 12 b provided on the tulip 12 a of the pedicle screw assembly 10.The purpose for this cooperation will be explained below.

The illustrated installation tool 140 also includes a rotation tool 142that is supported within the passageway 141 d of the installation tool140 for rotation relative to the body 141. The rotation tool 142includes a drive portion 142 a that extends outwardly from theexternally threaded portion 141 a at the first end of the body 141 and ahead portion 142 b that extends outwardly from the impaction surface 141c at the second end of the body 141. The drive portion 142 a of therotation tool 142 is preferably sized and shaped to cooperate with thedrive mechanism provided on the tip portions illustrated in FIGS. 10through 17. The purpose for this cooperation will also be explainedbelow. Lastly, the illustrated installation tool 140 includes animpaction cap 143 that sized and shaped to fit over the head portion 142b of the rotation tool 142 and to engage the impaction surface 141 c ofthe body 141. As shown in FIG. 18, an axial clearance is providedbetween the head portion 142 b of the rotation tool 142 and the innersurface of the impaction cap 143. The purpose of the impaction cap 143and this axial clearance will also be explained below.

The illustrated installation tool 140 can be used to facilitate theinstallation of the pedicle screw assembly as follows. If theinstallation tool 140 is being to install the embodiments of the pediclescrew assembly illustrated in FIGS. 1 through 9 (which do not include adrive mechanism provided on the tip portion), then the rotation tool 142and the impaction cap 143 can be initially removed. If, on the otherhand, the installation tool 140 is being to install the embodiments ofthe pedicle screw assembly illustrated in FIGS. 10 through 17 (which doinclude a drive mechanism provided on the tip portion), then therotation tool 142 and the impaction cap 143 can be retained as shown inFIG. 18.

In either event, the externally threaded portion 141 a of the body 141is threaded into the internal thread 12 b provided on the tulip 12 a ofthe pedicle screw assembly 10. Such threading is continued until theengagement surface 141 b of the body 141 engages the outermost end ofthe tulip 12 a. As a result of this threaded engagement, theinstallation tool 140 is securely connected to the pedicle screwassembly 10. Then, (if the rotation tool 142 and the impaction cap 143are to be used), the impaction cap 143 is disposed over the head portion142 b of the rotation tool 142 and into engagement with the impactionsurface 141 c of the body 141. The axial clearance provided between thehead portion 142 b of the rotation tool 142 and the inner surface of theimpaction cap 143 allows the rotation tool 142 to be retracted (eitherpartially or completely) inwardly within the externally threaded portion141 a of the body 141. Thereafter, an impact force (represented by thearrow in FIG. 18) is applied to the impaction cap 143 so as to advancethe extended tip portion of the pedicle screw assembly within thepedicle of the vertebra, as described above. The impaction cap 143 isthen removed, and the drive portion 142 a of the rotation tool 142 ismoved into cooperation with the drive mechanism provided on the tipportions illustrated in FIGS. 10 through 17. Lastly, the rotation tool142 is rotated (represented by the arrows in FIG. 19) by rotating thehead portion 142 b, such as by manual manipulation. Such rotation causesconcurrent rotation of the tip portion relative to the body portion ofthe pedicle screw assembly. As a result, the tip portion of the pediclescrew assembly can be manually moved from the extended position to theretracted position, as also described above, to allow the finalinstallation of the pedicle screw assembly.

The principle and mode of operation of this invention have beenexplained and illustrated in its preferred embodiments. However, it mustbe understood that this invention may be practiced otherwise than asspecifically explained and illustrated without departing from its spiritor scope.

1. A pedicle screw assembly comprising: a body portion including a headand a shank, the shank including an outer surface with a thread providedthereon, an end having a cutting tip provided thereon, and a boreextending inwardly from the end and having an internally threaded regionprovided therein; and a tip portion including a body having a cuttingedge and a shank extending from the body, the shank having an externallythreaded region provided thereon that cooperates with the internallythreaded region of the bore to permit movement of the tip portionrelative to the body portion between extended and retracted positions,wherein the internally threaded region of the bore has a firstinternally threaded region defined by a first diameter and a secondinternally threaded region defined by a second diameter that is largerthan the first diameter, and wherein the externally threaded region ofthe tip portion has first externally threaded region that cooperateswith the first internally threaded region of the bore and a secondexternally threaded region that cooperates with the second internallythreaded region of the bore.
 2. The pedicle screw assembly defined inclaim 1 wherein the bore further includes a non-threaded region that isprovided between the first internally threaded region and the secondinternally threaded region such that the tip portion can be locatedrelative to the body portion in an intermediate position between theextended and retracted positions.
 3. The pedicle screw assembly definedin claim 1 wherein the cutting edge of the tip portion includes a drilltip cutting edge and a clearance cutting edge.
 4. The pedicle screwassembly defined in claim 1 wherein the cutting edge of the tip portionincludes a beveled tip edge.
 5. The pedicle screw assembly defined inclaim 1 wherein the thread provided on the outer surface of the bodyportion includes a lead portion.
 6. The pedicle screw assembly definedin claim 5 wherein the thread provided on the outer surface of the bodyportion further includes a transition portion provided between thethread and the lead portion.
 7. The pedicle screw assembly defined inclaim 1 wherein the bore includes a reduced diameter portion thatextends from the internally threaded region and an enlarged diameterportion that extends from the reduced diameter portion, and wherein thetip portion further includes an extension that terminates in an enlargedend defining an outer diameter that is larger than the reduced diameterportion of the bore, but is smaller than the enlarged diameter portionof such bore.
 8. The pedicle screw assembly defined in claim 1 whereinthe tip portion further includes an extension that terminates in an endhaving a drive mechanism provided thereon.
 9. The pedicle screw assemblydefined in claim 1 wherein the tip portion includes a non-threadedregion between the second externally threaded region and the firstexternally threaded region.
 10. The pedicle screw assembly defined inclaim 1 wherein the thread provided outer surface of the shank of thebody portion has an enlarged diameter region located adjacent to thehead.